<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
    <style>
        .one {
            width: 100px;
            height: 100px;
            background-color: aqua;
        }
        .two {
            width: 100px;
            height: 100px;
            background-color: hotpink;
        }
        .three {
            width: 100px;
            height: 100px;
            background-color: yellowgreen;
        }
    </style>
</head>
<body>
    <div id="app">  
        <!-- class强制绑定写法：值是一个字符串 -->
        <div :class="className"></div>
    </div>
    <script>
        //
        const vm = new Vue({
            el:"#app",
            data() {
                return {
                    className:"three"
                }
            }
        })
    </script>
</body>
</html>